1. Field of the Invention
This invention relates to a dual window unit, and more particularly a dual window unit construction providing a unit for use in combination with an existing unit disposed in an opening in a building wall.
2. Prior Art
The type of exterior window units with which this invention is concerned provides a high degree of thermal insulation, air-tightness and sound insulation since the units are mounted on the outside of openings in building walls, in which openings other window assemblies have been previously installed.
When installing new exterior window units in combination with existing interior window units, it was required to reconstruct or break down the exterior sidings of the building walls or some of the frame members of the existing interior window units. Considerable difficulty was also experienced in mounting the vertical frames or jambs of the new units in cases where the exterior building walls vary in thickness, and thus the installation work was time-consuming and tedious.